The present invention relates to agricultural fertilizer applicators; and more particularly, to a fertilizer applicator in which the fertilizer is deposited in a trench or furrow formed behind a knife. The knife is located to follow behind a colter which cuts residue, and a closing assembly such as a packer wheel or other mechanism is typically located behind the knife to close the furrow after the fertilizer is deposited.
Typically, a number of separate applicator knives may be mounted to a common frame or tool bar which is pulled by a tractor and extends transversely of the direction of travel of the tractor. The applicator knives are spaced laterally so that a wide swath of land may be treated in a single pass of the tractor. The applicators may deposit liquid fertilizer in the form of anhydrous ammonia, dry fertilizer in pellet form, or a combination of both. The illustrated embodiment of the invention is designed for application of anhydrous ammonia. In this case, a tank of anhydrous ammonia may be carried by the same frame to which the tools are mounted or by a separate wheeled caddie which is pulled behind the tool bar and acts as a source of liquid fertilizer to supply each of the applicator knives.
One such applicator is disclosed in U.S. Pat. No. 3,799,079, issued Mar 26, 1974 for "Applicator for Depositing Anhydrous Ammonia Underground". As indicated in that patent, it is important to keep the knife aligned directly behind the oolter so that the knife follows directly in the cut line of the colter. Even a slight misalignment of the knife relative to the colter can cause residue or "trash", as it is sometimes called, to bridge across the knife, thereby increasing draft forces of the implement.
The problem of keeping the knife aligned with the coulter was addressed in the '079 patent, identified above. That apparatus was, however, used primarily in areas where moldboard plowing or other deep primary tillage was used. In that type of situation, the need for trash clearance between the coulter and knife was not as great as is currently found to exist because of changed farming practices. Today, more farmers are employing minimum tillage or even no tillage farming techniques, with the object of increasing the amount of crop residue lying on the surface after harvesting in hopes of reducing soil erosion. In short, what was acceptable trash clearance in agricultural equipment in the early 1970's may no longer be acceptable to many farmers. Acceptable trash clearance can be achieved by mounting the coulter and knife on separate tool bars spaced fore-and-aft, but that arrangement compounds the problem of alignment of knife and coulter, especially under hard use conditions. Further, using separate tool bars eliminates the convenience of adjusting lateral spacing between using simply by sliding one mounting assembly along its own toolbar.
In addition, in the '079 patent, a single spring cushion mechanism was used to bias both the coulter and the applicator knife into the use position. This had the effect of raising the knife when the coulter passed over an obstruction and raising the colter as the knife passed over the same obstruction. This had a tendency to increase the effective area of an obstruction and it also required that the same pre-load on the spring bias be effective for both the coulter and the knife. Farmers had no choice in the matter.